I've responded to a previous forum thread on this subject, but again, here's my two cents (or more like a whole quarter...)
1989 - Baseball foil [fixed rows of "UPPER DECK" right-side up & up-side down; moving baseball images (small) in background]
1990 - Baseball foil [two fixed rows of "UPPER DECK" up & down; moving baseball images (larger) in background AND moving "90 90 90" (wide spaced) seen in gaps between rows of text, swirling around the baseballs]
1990 - Comic Ball [two fixed rows of "UPPER DECK" up & down; background has sliding row of carrots (alternating up & down) that FLIP (i.e. change when viewed from a different angle) into an image of rows of "90 06 90 06" (narrow spaced) up & down]
1990 - Hockey [two fixed rows of "UPPER DECK" up & down; square-ish "90"s (look like jersey #s) in background AND crossed hockey sticks - harder to see, look like hexes, or chainlink fencing]
1991 - All products [fixed rows of "UPPER DECK" up & down, staggered and stacked like bricks in a wall; FLIP image is fixed lines of "91 16" (wide spaced) up & down]
1992 - All products [fixed Upper Deck DIAMOND LOGO, with 92 at bottom of diamond; NO alternate image]
1993 - All products [fixed Upper Deck DIAMOND LOGO, with 93 at bottom of diamond; FLIP image is brick wall of "UPPER DECK" text, up & down]
1994 - All products [last year-numbered DIAMOND LOGO, with 94...]
The most affected cards are the sets released between 1990 and 1992. Due to Upper Deck's propensity to release a Series 2, or High Number set (which included reprints of Low Number cards), several different rolls of foil were applied to cards, apparently at the whim of the factory workers. I think 1990-91 Hockey got the worst of it, with up to four different foils: 90 Hockey, 90 Baseball, 90 Comic Ball & 91 UD winding up on High Number release cards. 1991 Baseball has 90 Baseball & 91 UD. 1991 Football has several foils as well, but I don't have any "in hand" to verify. From the submitted scans, the "90" foil on 1991 Football looks like the jersey # style of hockey, does it have the hockey sticks on it, or did football have it's own "90" foil? The 1991-92 Hockey set has a mix of 91 & 92 foils.
Well, as far as my opinion on the classification of "VAR" or parallel set, I think it should be a parallel. Just like a Topps Gold card from that era, the only difference is in the foiling. One problem with scanning these is that you can't capture a moving/flipping hologram image in a single scan. It does help that the newer scans have the "zoom" feature, but if taken at the wrong angle, you may not see the difference.
As a team collector (old school N.J. Devils), I noticed that I have a few "carrots" in my collection. I would like to collect all the different foils, but with the redundancy of English & French already doubling up space in my binders for cards from that era, I'm not as focused on that objective.
I hope this helps clear the air a bit about the UD foil debate.